Corrugated pipe sections are used in the drainage of water-saturated soil in various agricultural, residential, recreational, or civil engineering and construction applications, such as for storm sewers. Corrugated pipe sections are also used for sanitary sewer pipe. Traditionally, drainage and sewer pipe was made from clay, concrete, or steel, which caused the pipe to be heavy, expensive, and brittle. In order to improve the cost-effectiveness, durability, and ease-of-installation of pipes, it is now common in the art to manufacture such pipes from alternative materials including various polymers and polymer blends.
Polymer pipe can be made by extruding raw polymer pellets into an annular tube of molten polymer, and then shaping it into a desired profile. The polymer pipe may also be made by co-extruding two annular tubes of molten polymer, and then shaping them together to form dual-wall pipe. One example of dual-wall polymer pipe is disclosed in U.S. patent application Ser. No. 11/078,323, filed on Mar. 15, 2005 by Goddard et al. In some cases, it may be desirable to improve the strength and resistance to deformation of such pipe in order to further improve its competitive advantage over traditional concrete drainage pipe.
Some attempts have been made at creating stronger pipe sections having three-walls, with a corrugated wall between two smooth walls. Such three-wall pipe has never before been successfully created in diameters larger than 14 inches, making it unsuitable for large diameter applications. Moreover, the attempts at making three-wall pipe have always involved the use of a sizing mandrel to create a smooth outer wall, which is insufficient in strength for large diameter applications.
After extrusion and molding, plastic pipe is often cut to form relatively light, manageable, and transportable sizes of pipe sections, ranging from a few feet to many yards in length. Once these plastic pipe sections are transported to their desired installation location, they are assembled lengthwise by the installation of joints, adhesives, or other coupling means. This coupling process has generally been complex, requiring the transportation of many tools and supplies to the job site, and has required many man-hours for completion.
For example, one method of assembly involves the formation of a wide-diameter bell at one end of each plastic pipe section. During the pipe manufacturing process, an apparatus known as a “beller” is sometimes used to radially expand the end of the pipe, forming an expanded bell-shaped structure, such that the opposite end of an adjacent pipe section may be inserted into the expanded bell-shaped end. Alternatively, bell and spigot portions are affixed to pipe sections, e.g., using a hot plate welder, or the like. These processes have several disadvantages, including weaknesses that require additional means of reinforcement, such as external straps, hinged brackets, overlapping wraps, shrink-wrap layers, or a combination of such reinforcement means. Finally, these bells and other known coupling means require precise and careful excavation, installation, and backfill, to avoid misalignment between pipe sections and expanded coupling sections during assembly and placement. The improper installation of these coupling means often results in joint failure, buckling, and an inability to form a water-tight seal between adjacent pipe sections.
One example of an improved water-tight, in-line, bell and spigot, which can be used for coupling sections of three-wall, corrugated pipe, was disclosed in U.S. patent application Ser. No. 11/941,605, filed by Gerald S. Sutton et al. on Nov. 16, 2007. In order to create pipe sections having such a water-tight, in-line bell and spigot at either end, there is a need to extrude an outer wall of plastic onto a dual-wall corrugated pipe having in-line bell and spigot preforms. The three-wall pipe can then be cut between adjacent in-line bells and spigots. However, the creation of three-wall corrugated pipe involves many challenges, especially in large diameter applications.
Accordingly, there is a need for improved systems and methods for making multi-wall corrugated polymer pipe.